1. Field of the Invention
This invention relates to a process for producing a transparent glass fiber-reinforced resin molded sheet which is especially suitable as a roofing sheet, a sidewall sheet, etc., of a greenhouse. The sheet is prepared from a resin composed mainly of acrylic acid, methacrylic acid or an ester thereof, typified by methyl methacrylate.
In this specification, the term "acrylate" is used collectively to refer to both acrylic and methacrylic acid as well as esters thereof.
2. Description of the Prior Art
Molded articles from glass fiber-reinforced resins obtained by impregnating glass fibers with a resin composed mainly of methyl methacrylate and curing the resin have frequently been used outdoors as sheet-like molded articles. A technique is known to obtain a transparent molded article of a fiber glass-reinforced resin by bringing the refractive index of the resin into agreement with that of the glass forming the glass fibers. According to one example of such a technique, methyl methacrylate is copolymerized with a vinyl aromatic hydrocarbon such that the refractive index of the methyl methacrylate polymer (about 1.49) is adjusted with the high refractive index of the vinyl aromatic hydrocarbon polymer (about 1.58 to 1.60) to bring the refractive index of the resin into agreement with that of glass fibers (1.515 to 1.520). See, for example, R. B. Beevers, Trans. Faraday Soc., 58, 1465 (1962). However, the rate of polymerization of the vinyl aromatic hydrocarbon is slow and, as a result, a viscous solution or a resin syrup obtained by partial copolymerization of the two monomers and with which the glass fibers are to be impregnated takes too long to cure, which has been a principal drawback in methods of producing glass fiber-reinforced resin products efficiently.
Japanese Patent Publication No. 15909/1969 discloses a resin syrup for use in preparing transparent moldings or laminates. The resin syrup is a composition of an acrylonitrile-styrene copolymer containing 17 to 40 mol% acrylonitrile dissolved in methyl methacrylate monomer or a monomer mixture containing methyl methacrylate. The viscosity of the resin syrup is 0.1 to 50 poise at 20.degree. C.